Changes In CO2 Concentration Research Articles

Meridional structure and future changes of tropopause height and temperature

We use a simple, semianalytic, column model to understand better the meridional structure of the tropopause height and future changes in its height and temperature associated with global warming. The model allows us to separate the effects of tropospheric lapse rate, optical depth, outgoing longwave radiation (OLR), and stratospheric cooling on the tropopause height. When applied locally at each latitudinal band, the model predicts the overall meridional structure of the tropopause height, with a tropical tropopause substantially higher than in higher latitudes and a sharp transition at the edge of the extratropics. The large optical depth of the Tropics, due mainly to the large water‐vapour path, is the dominant tropospheric effect producing the higher tropical tropopause, whereas the larger tropical lapse rate actually acts to lower the tropopause height. The dynamical cooling induced by the stratospheric circulation lifts the thermal tropopause in the Tropics further, resulting in it being significantly cooler and higher than in mid‐ and high‐latitudes.The model quantifies the causes of the tropopause height increase with global warming that is found robustly in climate integrations from the fifth Coupled Model Intercomparison Project (CMIP5). The large spread in the increase rate of tropopause height in the CMIP5 model is captured by the simple model, which attributes the dominant contributions to changes in water‐vapour path and lapse rate, with changes in CO2 concentration and OLR having much smaller direct effects. The CMIP5 models also show a small but robust increase in the tropopause temperature in low latitudes, with a much smaller increase in higher latitudes. We suggest that the tropical increase may be caused at least in part by nongrey effects in the radiative transfer associated with the higher levels of water vapour in the Tropics, with near‐constant tropopause temperatures predicted otherwise.

Future Carbon Emission From Boreal and Permafrost Lakes Are Sensitive to Catchment Organic Carbon Loads

AbstractCarbon storage, processing, and transport in freshwater systems are important components of the global carbon cycle and sensitive to global change. However, in large‐scale modeling this part of the boundless carbon cycle is often lacking or represented in a very simplified way. A new process‐oriented lake biogeochemical model is used for investigating impacts of changes in atmospheric CO2 concentrations and organic carbon loading from the catchment on future greenhouse gas emissions from lakes across two boreal to subarctic regions (Northern Sweden and Alaska). Aquatic processes represented include carbon, oxygen, phytoplankton, and nutrient dynamics leading to CO2 and CH4 exchanges with the atmosphere. The model is running inside a macroscale hydrological model and may be easily implemented into a land surface scheme. Model evaluation demonstrates the validity in terms of average concentration of nutrients, algal biomass, and organic and inorganic carbon. Cumulative annual emissions of CH4 and CO2, as well as pathways of CH4 emissions, also compare well to observations. Model calculations imply that lake emissions of CH4 may increase by up to 45% under the Representative Concentration Pathway 8.5 scenario until 2100, and CO2 emissions may increase by up to 80% in Alaska. Increasing organic carbon loading to the lakes resulted in a linear response in CO2 and CH4 emissions across both regions, but increases in CO2 emissions from subarctic lakes in Sweden were lower than for southern boreal lakes, probably due to the higher importance of imported vegetation‐“generated” inorganic carbon for CO2 emission from subarctic lakes.

Effects of carbonic anhydrase inhibition on biomass and primary production of estuarine benthic microalgal communities

Recent studies have focused on carbon concentrating mechanisms and the associated enzyme, carbonic anhydrase, to better understand the efficiency of CO2 uptake rates and carbon fixation in photoautotrophs. Some benthic microalgae (BMA) may be limited by inorganic carbon availability because high photosynthetic rates withdraw a large amount of CO2 and HCO3– in the top layer of sediment. Investigating the mechanisms that affect carbon acquisition are necessary if we are to fully understand the functioning and structuring processes of these systems. From this, we can better predict the potential impacts of increasing atmospheric CO2 concentrations on BMA communities. The purpose of this research was to examine a carbon concentrating mechanism used by BMA through their responses to induced carbon limitation. This approach was conducted through the removal of carbonic anhydrase (CA) activity using an inhibitor, ethoxyzolamide. Microcosm experiments were performed on intertidal muddy sediments from North Inlet Estuary, SC. Exposure to ethoxyzolamide resulted in a reduction of gross primary productivity (GPP) without a reduction in total BMA biomass. Furthermore, removed CA activity caused BMA cumulative GPP maxima to shift upward toward the surface in the sediment column. Active CA was necessary to maintain high GPP rates in these communities and allowed motile BMA to use a wider portion of the sediment column. Available HCO3– at lower depths could still be dehydrated into CO2 by microalgae with CA. Changes in global atmospheric CO2 concentrations leading to higher CO2 availability at the atmosphere-sediment interface may alter the structure and function of these BMA systems, and the vertical distribution of GPP. These consequences may have important implications for the biogeochemical cycling occurring in estuaries.

Accumulation of soil carbon under elevated CO2 unaffected by warming and drought.

Elevated atmospheric CO2 concentration and climate change may substantially alter soil carbon (C) dynamics, which in turn may impact future climate through feedback cycles. However, only very few field experiments worldwide have combined elevated CO2 (eCO2 ) with both warming and changes in precipitation in order to study the potential combined effects of changes in these fundamental drivers of C cycling in ecosystems. We exposed a temperate heath/grassland to eCO2 , warming, and drought, in all combinations for 8years. At the end of the study, soil C stocks were on average 0.927kgC/m2 higher across all treatment combinations with eCO2 compared to ambient CO2 treatments (equal to an increase of 0.120±0.043kgCm-2 year-1 ), and showed no sign of slowed accumulation over time. However, if observed pretreatment differences in soil C are taken into account, the annual rate of increase caused by eCO2 may be as high as 0.177±0.070kgCm-2 year-1 . Furthermore, the response to eCO2 was not affected by simultaneous exposure to warming and drought. The robust increase in soil C under eCO2 observed here, even when combined with other climate change factors, suggests that there is continued and strong potential for enhanced soil carbon sequestration in some ecosystems to mitigate increasing atmospheric CO2 concentrations under future climate conditions. The feedback between land C and climate remains one of the largest sources of uncertainty in future climate projections, yet experimental data under simulated future climate, and especially including combined changes, are still scarce. Globally coordinated and distributed experiments with long-term measurements of changes in soil C in response to the three major climate change-related global changes, eCO2 , warming, and changes in precipitation patterns, are, therefore, urgently needed.

Effect of Metal Loading in Unpromoted and Promoted CoMo/Al2O3–TiO2 Catalysts for the Hydrodeoxygenation of Phenol

This paper reports the effects of changes in the supported active phase concentration over titania containing mixed oxides catalysts for hydrodeoxygenation (HDO). Mo and CoMo supported on sol–gel Al2O3–TiO2 (Al/Ti = 2) were synthetized and tested for the HDO of phenol in a batch reactor at 5.5 MPa, 593 K, and 100 ppm S. Characterization results showed that the increase in Mo loading led to an increase in the amount of oxide Mo species with octahedral coordination (MoOh), which produced more active sites and augmented the catalytic activity. The study of the change of Co concentration allowed prototypes of the oxide species and their relationship with the CoMo/AT2 activity to be described. Catalysts were tested at four different Co/(Co + Mo) ratios. The results presented a correlation between the available fraction of CoOh and the catalytic performance. At low CoOh fractions (Co/(Co + Mo) = 0.1), Co could not promote all MoS2 slabs and metallic sites from this latter phase performed the reaction. Also, at high Co/(Co + Mo) ratios (0.3 and 0.4), there was a loss of Co species. The Co/(Co + Mo) = 0.2 ratio presented an optimum amount of available CoOh and catalytic activity since the XPS results indicated a higher concentration of the CoMoS phase than at a higher ratio.

Optimization and control of the light environment for greenhouse crop production

Optimization and control of the greenhouse light environment is key to increasing crop yield and quality. However, the light saturation point impacts the efficient use of light. Therefore, the dynamic acquisition of the light saturation point that is influenced by changes in temperature and CO2 concentration is an important challenge for the development of greenhouse light environment control system. In view of this challenge, this paper describes a light environment optimization and control model based on a crop growth model for predicting cucumber photosynthesis. The photosynthetic rate values for different photosynthetic photon flux densities (PPFD), CO2 concentration, and temperature conditions provided to cucumber seedlings were obtained by using an LI-6400XT portable photosynthesis system during multi-factorial experiments. Based on the measured data, photosynthetic rate predictions were determined. Next, a support vector machine(SVM) photosynthetic rate prediction model was used to obtain the light response curve under other temperatures and CO2 conditions. The light saturation point was used to establish the light environment optimization and control model and to perform model validation. The slope of the fitting straight line comparing the measured and predicted light saturation point was 0.99, the intercept was 23.46 and the coefficient of determination was 0.98. The light control model was able to perform dynamic acquisition of the light saturation point and provide a theoretical basis for the efficient and accurate control of the greenhouse light environment.

Optical fiber carbon dioxide sensor based on colorimetric change of α-naphtholphthalein and CIS/ZnS quantum dots incorporated with a polymer matrix

This paper presents a new optical fiber carbon dioxide (CO2) sensor based on the emission wavelength shift of CuInS2/ZnS quantum dots (CIS/ZnS QDs) due to changes in the absorption of a pH indicator (α-naphtholphthalein) with a changing CO2 concentration. Using an LED with a central wavelength of 375 nm as the excitation source, it is shown that using the red emission of CIS/ZnS QDs allows for the detection of CO2 concentration over the range of 0-100%, and the associated wavelength shift was found to be 630 pm/%CO2. Moreover, the observed luminescence intensity from CIS/ZnS QDs at 578 nm increases as the CO2 concentration increases. The observed luminescence intensity change by CO2 is expressed as I100/I0, which I0 is used to represent the sensitivity of the optical fiber sensor, where I100 and I0 represent the steady-state luminescence intensities in pure carbon dioxide and pure nitrogen environments, respectively. The ratio I100/I0 of this optical fiber sensor is estimated to be 100. These results of the optical sensing method can be used in practice for detection of CO2 and could offer a new approach for developing novel types of optical fiber sensor.

Elevated CO2 concentration induces photosynthetic down-regulation with changes in leaf structure, non-structural carbohydrates and nitrogen content of soybean

BackgroundUnderstanding the mechanisms of crops in response to elevated CO2 concentrations is pivotal to estimating the impacts of climate change on the global agricultural production. Based on earlier results of the “doubling-CO2 concentration” experiments, many current climate models may overestimate the CO2 fertilization effect on crops, and meanwhile, underestimate the potential impacts of future climate change on global agriculture ecosystem when the atmospheric CO2 concentration goes beyond the optimal levels for crop growth.ResultsThis study examined the photosynthetic response of soybean (Glycine max (L.) Merr.) to elevated CO2 concentration associated with changes in leaf structure, non-structural carbohydrates and nitrogen content with environmental growth chambers where the CO2 concentration was controlled at 400, 600, 800, 1000, 1200, 1400, 1600 ppm. We found CO2-induced down-regulation of leaf photosynthesis as evidenced by the consistently declined leaf net photosynthetic rate (An) with elevated CO2 concentrations. This down-regulation of leaf photosynthesis was evident in biochemical and photochemical processes since the maximum carboxylation rate (Vcmax) and the maximum electron transport rate (Jmax) were dramatically decreased at higher CO2 concentrations exceeding their optimal values of about 600 ppm and 400 ppm, respectively. Moreover, the down-regulation of leaf photosynthesis at high CO2 concentration was partially attributed to the reduced stomatal conductance (Gs) as demonstrated by the declines in stomatal density and stomatal area as well as the changes in the spatial distribution pattern of stomata. In addition, the smaller total mesophyll size (palisade and spongy tissues) and the lower nitrogen availability may also contribute to the down-regulation of leaf photosynthesis when soybean subjected to high CO2 concentration environment.ConclusionsDown-regulation of leaf photosynthesis associated with the changes in stomatal traits, mesophyll tissue size, non-structural carbohydrates, and nitrogen availability of soybean in response to future high atmospheric CO2 concentration and climate change.

The response of carbon stocks of drylands in Central Asia to changes of CO2 and climate during past 35 years

Drylands are terrestrial ecosystems sensitive to climate change. There are totally drylands of 5.17 × 106 km2 (above 80% of global total temperate desert area) in Central Asia (CAS), in which significant increases of temperature and changes of precipitation have been detected in recent decades. However, environment-induced changes in terrestrial carbon stocks of these dryland ecosystems have not been well investigated. With the Arid Ecosystem Model (AEM), this study was devoted to analyze spatiotemporal changes of carbon stocks in drylands over CAS during the past 35 years (1980–2014) and to quantify contributions to these changes of various factors, including temperature, precipitation, and atmospheric CO2 concentration. Over the study period, total stocks of vegetation carbon (VEGC), soil organic carbon (SOC), and litter carbon (LTRC) averaged 2.8 ± 0.05 Pg C, 45.2 ± 0.01 Pg C, and 0.3 ± 0.004 Pg C(1Pg = 1015 g) in CAS, respectively. Meanwhile, total carbon (TOTC) declined by 0.7 Pg C. Climate change caused TOTC to decrease by 1.3 Pg C. In contrast, CO2 enrichment effect caused TOTC to increase by 0.9 Pg C. The effects of different factors on TOTC changes varied spatially. Precipitation was the dominant factor regulating TOTC change in 40.9% of the study area, mainly in the desert sparse shrub region in northwest Kazakhstan and the dryland region of southern Xinjiang of China, in which vegetation growth was mainly limited by water resource. CO2 dominated the change of TOTC in 38.3% of the study area, mainly in the lower altitude regions of Tianshan mountain, in which the hydrothermal condition was relatively suitable for vegetation growth. Ecosystems in southern Xinjiang of China and northwest Kazakhstan are fragile to climate change.

Impacts of Change in Atmospheric CO2 Concentration on Larix gmelinii Forest Growth in Northeast China from 1950 to 2010

Although CO2 fertilization on plant growth has been repeatedly modeled to be the main reason for the current changes in the terrestrial carbon sink at the global scale, there have been controversial findings on the CO2 fertilization effects on forests from tree-ring analyses. In this study, we employed conventional dendrochronological tree-ring datasets from Northeast China, to detect the effect of CO2 fertilization on Larix gmelinii growth from 1950 to 2010. Among four sites, there were two sites exhibiting a significant residual growth enhancement at a 90% confidence level after removing the size, age and climaterelated trends of tree-ring indices. In addition, we found consistency (R from 0.26 to 0.33, p < 0.1) between the high frequency CO2 fluctuation and residual growth indices at two of the four sites during the common period. A biogeochemical model was used to quantitatively predict the contribution of elevated atmospheric CO2 on accumulated residual growth enhancement. As found in the tree-ring data, 14% of the residual growth was attributed to the CO2 fertilization effect, while climate was responsible for approximately the remainding 86%.

Effect of CO2 on the properties of anion exchange membranes for fuel cell applications

In this study the effect of CO2, HCO3‾ and CO32‾ on the ionic conductivity and water uptake properties of anion exchange membranes (AEMs) was investigated in order to better understand the detrimental effect of ambient air feed on the performance of AEM fuel cells. Three types of AEMs were examined, including Poly(hexamethyl-p-terphenyl benzimidazolium) (HMT-PMBI), Fumatech® FAA-3, and poly(phenylene oxide) functionalized with imidazole (PPO-Im). The effect of temperature and humidity on AEM properties in their different anion forms was studied, including both steady state and dynamic measurements. In addition, the response to changes in CO2 concentration and to application of ex-situ electric current was examined. Results showed that an increase in humidity leads to an increase in water content and an increase in conductivity of the AEMs, regardless the anion type. It was found that both temperature and relative humidity improve conductivity in carbonated forms, however relative humidity has the most significant impact. The carbonation process in 400 ppm CO2 is slightly quicker in AEMs with low conductivity, lasting ca. 40 min; however it was shown that a reverse process can be achieved by applying an electric current through the AEMs. An increase by 2–10 fold in conductivity is obtained using this method, which is analogous to the changes observed during operation of the fuel cell. This work provides important data that needs to be taken into account in future work in order to ultimately mitigate the carbonation effects and improve the performance of AEM fuel cells running with ambient air.

Simulating Rangeland Ecosystems with G-Range: Model Description and Evaluation at Global and Site Scales

Rangeland ecosystems and their roles in providing ecosystem services are vulnerable to changes in climate, CO2 concentration, and management. These drivers forcing widespread changes in rangeland ecosystem processes and vegetation dynamics create two-way interactions and feedback loops between biogeochemistry and vegetation composition. To support spatial simulation and forecasting in the global rangelands, the G-Range global rangelands model couples biogeochemical submodels from the CENTURY soil organic matter model with dynamic populations’ submodels for herbs, shrubs, and trees. Here is presented a model description for G-Range, including novel elements of G-Range and implementation of CENTURY code. An initial evaluation of G-Range at global and site scales follows. G-Range outputs for net primary productivity (NPP) and vegetation cover (herbs, shrubs, trees, bare ground) were evaluated against global MODIS layers at global and site scales, and aboveground and belowground NPP were compared with field data from globally distributed sites. Most model outputs evaluated were within the range of a priori benchmarks for tolerable absolute or relative error (two benchmarks per output, at two scales, for five outputs of NPP and vegetation cover). Trade-offs in model fit among variables, datasets, and scales indicated practical constraints on improving model fit with respect to the selected evaluation datasets, especially field NPP versus MODIS NPP. The relative effects of multiple drivers of rangeland vegetation change were the greatest sources of uncertainty in model outputs. G-Range is best suited to scenario analysis of large-scale and long-term impacts of climate, CO2, and management on rangeland ecosystem processes and vegetation, as well as ecosystem services, such as production of forage and browse and carbon sequestration.

Methodological clarification for estimating the input of plant-derived carbon in soils under elevated CO2 based on a 13C-enriched CO2 labeling experiment

BACKGROUND AND AIMS: Under the scenario of global change, continuous ¹³C-enriched CO₂ labeling is a powerful tool for evaluating the interaction between plants and soil, especially the influence of elevated CO₂ on the input of plant-derived C (new C) into soil in the short term. However, the methodological validity concerning the acquisition of isotopic signals and their implications in plants and soil remains ambiguous. METHODS: We conducted an experiment simulating elevated CO₂ with wheat planted in growth chambers. ¹³C-enriched CO₂ with identical ¹³C abundance was supplied at two CO₂ concentration levels (350 versus 600 ppm) until wheat harvest. The δ¹³C values of plant tissues and soil were measured periodically during the growing season. RESULTS: The δ¹³C values of wheat tissues under elevated ¹³CO₂ were 15–17% higher than those under ambient ¹³CO₂ after the heading stage, implying that the ¹³C signals themselves in plants and soil were not directly representative of the influence of elevated CO₂ on the C fixation in the plant and thereby the flow of plant-derived C into soil. The proportion of plant-derived C in the soil (fₙₑw) was calculated separately at each CO₂ concentration by taking the initial soil as a reference and the corresponding δ¹³C values as parameters in the mixing model, and we found that elevated CO₂ significantly enhanced the new soil C input by approximately 35.5% during our 62-day labeling. In our experiment, the fₙₑw value under elevated CO₂ could be overestimated by up to 1.7 times if the alteration of ¹³C signatures in photosynthates caused by the change in CO₂ concentration is ignored. CONCLUSIONS: For methodological clarification, we suggest that 1) ¹³C labeling is essential in all CO₂ treatments to achieve CO₂ concentration-dependent ¹³C signals in plants and soil, and that 2) the influence of elevated CO₂ on soil C turnover can be estimated by the difference in the fₙₑw under the two CO₂ concentrations.

Air quality impacts of open-plan cooking in tiny substandard homes in Hong Kong

This study investigated the air quality impacts of open-plan cooking in subdivided units (SDUs), which is a type of substandard housing in Hong Kong. About 210,000 persons (2.9% of the population) currently live in such tiny and poorly ventilated dwellings. With a median floor area of merely 9.3 m2 (100 ft2), most SDUs do not have space for a partitioned kitchen to contain the air pollutants generated by cooking, posing a serious indoor air quality issue that affects all members living in the SDU. The CO, CO2, PM10, PM2.5 and VOC concentrations in seven SDUs were monitored for 72 h to capture the emissions from their routine cooking activities. All SDUs used induction or electric cookers and 32 cooking events were recorded. Under natural ventilation, the mean PM10 and PM2.5 concentrations during cooking were 36 and 20 μg/m3, which were 136% and 82% higher than the pre-cooking levels respectively. Their mean maximum concentrations reached 1644 and 749 μg/m3 respectively. The mean PM10 concentration exceeded the local guideline (excellent class) by 1.82 times. However, cooking activities did not contribute to substantial changes in CO, CO2 and VOC concentrations. When the air conditioner was turned on to relieve the heat from cooking, it took 90 min for air pollution to return to pre-cooking levels after a cooking event because of poor ventilation, which significantly increased the occupants’ exposure to the cloistered air pollutants. Lacking a partitioned kitchen and effective ventilation in SDUs may pose chronic health threats to their occupants, particularly children.

Mycorrhizal‐mediated plant–herbivore interactions in a high CO2 world

Abstract The symbiotic relationship between terrestrial plants and arbuscular mycorrhizal (AM) fungi is a key driver of plant nutritional and defence traits influencing insect herbivory. These tripartite interactions have been fundamental to shaping the evolution of land plants and the diversity of insect herbivores. Surprisingly, we have little understanding of how these interactions will function under elevated atmospheric CO2 concentrations (eCO2), despite the considerable implications for both natural and managed ecosystems. Although substantial research has revealed how eCO2 alters mycorrhizal–plant interactions, or plant–herbivore interactions, there is a stark scarcity of studies which investigate how eCO2 impacts mycorrhizal‐mediated plant–insect herbivore relationships. Here, we synthesise some of the main effects of eCO2 on the mycorrhizal symbiosis, the concomitant impacts on plant nutrient dynamics and secondary metabolism, and how eCO2‐driven changes in plant growth, biochemistry and communities impact insect herbivores. We point out that potential mechanistic drivers of AM fungal–plant–insect herbivore relationships under eCO2 can function antagonistically and are highly context‐dependent, which poses a particular challenge. Still, we hypothesise as to the potential outcomes for AM fungal–plant–herbivore dynamics under eCO2. We identify key research priorities to tackle the substantial gap in our understanding. If ecological theory is to effectively inform agricultural and natural management practices in the future, research needs to directly investigate how changes in global atmospheric CO2 concentrations impact the tripartite relationship between AM fungi, plants and insect herbivores. A plain language summary is available for this article.

A Carbon Flux Assessment Driven by Environmental Factors Over the Tibetan Plateau and Various Permafrost Regions

AbstractIn this study, the spatiotemporal changes in net primary production (NPP) and drivers, including climate change, atmospheric CO2 concentration and land use change, over the Tibetan Plateau from 1979 to 2016 were investigated using the version 4.5 of the Community Land Model. Based on high‐resolution atmospheric forcing data, six numerical experiments were designed to assess the relative contribution of different environmental factors on NPP. Our simulation results suggest that NPP over the Tibetan Plateau has increased significantly at a rate of 2.25 Tg C/year2 since 1979. At the plateau scale, changes in precipitation, CO2 concentration, and land use change contributed approximately 63.3%, 16.7%, and 9.5% to the interannual variation of NPP, respectively. Temperature did not exert a significant effect on the trends of NPP, which results from the increasing temperature enhancing the autotrophic respiration (AR) more than the gross primary production. We also divided the alpine grasslands into four types, including alpine meadow of permafrost, alpine steppe of permafrost, alpine meadow of seasonal frost, and alpine steppe of seasonal frost. We found that the increasing rate of NPP in permafrost regions was significantly higher than that in seasonal frost regions. Compared with other factors, precipitation change played a dominant role in the NPP over the four different types of grasslands. Temperature‐induced change on NPP and AR was larger in the alpine meadow regions compared to in the alpine steppe regions. In addition, NPP and AR showed a more remarkable response to temperature change over alpine meadow of permafrost than other regions.

Difference in the relationship between soil CO2 concentration and the karst-related carbon cycle under different land use types in southwest China

As an important driving force for karstification, soil CO2 has a close relation with karst-related carbon cycle. However, their relationship may be disturbed when H2SO4 and HNO3 participate in karstification. Here, soil CO2 and spring water samples were collected from two catchments to examine the dynamics of carbon under different land use types. The net CO2 consumption at the Baishuwan spring catchment (BSW; range 1.7–2.69 mmol/L, average of 2.21 mmol/L) was higher than it was at the Hougou spring catchment (HG; range − 0.63 to 0.02 mmol/L, average of − 0.24 mmol/L). Due to the participation of H2SO4 and HNO3, CO2 was released from bedrock and reduced net CO2 consumption when this portion of CO2 escaped from the water. With regard to soil CO2 concentration, a bidirectional gradient of CO2 concentration occurred at BSW, while alternating bidirectional and unidirectional gradients occurred at HG. However, the δ13C of soil CO2 could not confirm whether the vertical changes in soil CO2 concentration as well as net CO2 consumption were related to the CO2 released from bedrock to soil. With regard to seasonal changes, net CO2 consumption was consistent with soil CO2 concentration at BSW, while the reverse relationship was found at HG. These observations indicated that soil CO2 concentration was not the dominant factor controlling net CO2 consumption at HG, which was affected by H2SO4 and HNO3, and more CO2 escaped from the water due to the reduced water–rock reaction time in the rainy season.

Dynamics of greenhouse gases in groundwater: hydrogeological and hydrogeochemical controls

In this study the variability of greenhouse gases (GHGs) concentrations along lateral and vertical dimensions of the chalk aquifer located in the eastern part of Belgium was examined in order to understand its dependence on hydrogeological and hydrogeochemical conditions. Groundwater samples from 29 wells/piezometers were analyzed for concentrations of nitrous oxide (N2O), carbon dioxide (CO2), methane (CH4), major and minor elements and stable isotopes of nitrate (NO3−), nitrous oxide (N2O), sulfate (SO42−) and boron (B). For lateral investigations, four zones with different environmental settings were identified (southern, central, north-eastern and northern). Groundwater was oversaturated with GHGs with respect to its equilibrium concentrations with the atmosphere in all zones, except the northern one, undersaturated in N2O (0.07 ± 0.08 μgN/L vs. 0.3 μgN/L). Vertical dimension studies showed the decrease in CO2 concentration and significant changes in both isotope signatures and concentration of N2O with depth. The production of N2O could be attributed to a combination of nitrification and denitrification processes occurring at different depths. CO2 concentration is controlled by the process of dissolution of carbonate minerals which constitute aquifer geology. CH4 is produced due to methanogenesis in deeper parts of the aquifer, though its thermogenic origin is also possible. Differences in hydrogeochemical settings and changing intensity of biogeochemical processes across the area and with depth have considerable effect on GHGs concentrations. Thus, before estimating GHGs fluxes at the groundwater–river interface insights obtained from larger-scale investigations are required in order to identify the representative spatial zones which govern GHGs emissions.

Dynamic CO2 and pH levels in coastal, estuarine, and inland waters: Theoretical and observed effects on harmful algal blooms

Rising concentrations of atmospheric CO2 results in higher equilibrium concentrations of dissolved CO2 in natural waters, with corresponding increases in hydrogen ion and bicarbonate concentrations and decreases in hydroxyl ion and carbonate concentrations. Superimposed on these climate change effects is the dynamic nature of carbon cycling in coastal zones, which can lead to seasonal and diel changes in pH and CO2 concentrations that can exceed changes expected for open ocean ecosystems by the end of the century. Among harmful algae, i.e. some species and/or strains of Cyanobacteria, Dinophyceae, Prymnesiophyceae, Bacillariophyceae, and Ulvophyceae, the occurrence of a CO2 concentrating mechanisms (CCMs) is the most frequent mechanism of inorganic carbon acquisition in natural waters in equilibrium with the present atmosphere (400 μmol CO2 mol−1 total gas), with varying phenotypic modification of the CCM. No data on CCMs are available for Raphidophyceae or the brown tide Pelagophyceae. Several HAB species and/or strains respond to increased CO2 concentrations with increases in growth rate and/or cellular toxin content, however, others are unaffected. Beyond the effects of altered C concentrations and speciation on HABs, changes in pH in natural waters are likely to have profound effects on algal physiology. This review outlines the implications of changes in inorganic cycling for HABs in coastal zones, and reviews the knowns and unknowns with regard to how HABs can be expected to ocean acidification. We further point to the large regions of uncertainty with regard to this evolving field.

Atmospheric CO₂ Concentration and Other Limiting Factors in the Growth of C₃ and C₄ Plants.

It has been widely observed that recent increases in atmospheric CO2 concentrations have had, so far, a positive effect on the growth of plants. This is not surprising since CO2 is an important nutrient for plant matter, being directly involved in photosynthesis. However, it is also known that the conditions which have accompanied this increase in atmospheric CO2 concentration have also had significant effects on other environmental factors. It is possible that these other effects may emerge as limiting factors which could act to prevent plant growth. This may involve complex interactions between prevailing sunlight and water conditions, variable temperatures, the availability of essential nutrients and the type of synthetic pathway for the plant species. The issue of concern to this investigation is if we should be worried about a possible shift in the C3-C4 paradigm driven by changes in the atmospheric CO2 concentration, or if some other factor, such as water scarcity, is much more relevant within a 30-year time frame. If an opinion is needed on what will have the worst effect on the survival of the planet between the scarcity of water or the reduced efficiency of C3 plants to sequester CO2, the issue of water is the more incisive.